Diving suits are relatively thick to protect divers from the coldness of the water. Thus, when a diver puts on his diving suit, he needs to be able to increase the length of his diving watch bracelet so as to be able to put it around his wrist, over his diving suit.
For this purpose, it is known for diving watch bracelets to be fitted with a device known as a “diver's extension” for increasing the length of the bracelets of such diving watches. This extension conventionally includes a first adjusting link fitted with first and second parallel hinge pins extending transversely to the bracelet. The first adjusting link is connected to a link of one of the bracelet strands by the first hinge pin. The first adjusting link is associated with a second adjusting link by the second hinge pin. The second adjusting link is connected in turn to the cover of a clasp by a third hinge pin. Depending upon the respective position of the first and second adjusting links, the length of the bracelet varies between a first short adjustment size wherein the first and second links are superposed on each other in the clasp cover, and a second long adjustment size in which the first and second adjusting links are unfolded.
The diver's extension device includes a means of locking the first and second adjusting links in the short bracelet length adjustment position. In a known embodiment, this locking means is provided on the first adjusting link and includes firstly a tongue and secondly a pair of ball catches. More specifically, the tongue is provided in the extension of the first adjusting link, where the first adjusting link is hinged on the second adjusting link, whereas the ball catches are provided on the sides of the first adjusting link, in proximity to the area where the first adjusting link is connected to the end link of the bracelet strand to which the diver's extension device is hinged. The tongue is arranged to engage in a housing disposed in the clasp cover. To allow this movement of engagement, the second adjusting link must be folded down inside the clasp cover, while the first adjusting link must be presented substantially perpendicular to the plane of the clasp cover before being folded down onto the second adjusting link. If the first adjusting link is presented perpendicular to the plane of the clasp cover, the tongue is opposite the housing arranged inside the cover, and is then gradually engaged in the housing as the first adjusting link is folded onto the second adjusting link. The second adjusting link takes the form of a stretcher like frame between the arms of which the first adjusting link is housed. When the first adjusting link is almost folded down onto the second adjusting link, the ball catches provided on the flanks of the first adjusting link move back slightly, ensuring that the first adjusting link is held by friction on the second adjusting link.
The locking means described above has three drawbacks. First of all, the first adjusting link has to be presented in a well defined position, in this case substantially perpendicular to the plane of the clasp cover, so that the tongue can engage properly in the corresponding housing. If this condition is not satisfied, the diver's extension is not properly closed and the bracelet may open inadvertently, which means that the watch may be lost. Next, the order in which the two locking means, namely the tongue and the two ball catches, are operated cannot be changed. The tongue must first of all be engaged in its housing, and then it is only the ball catches which can lock the first adjusting link onto the second adjusting link. The reverse is not possible. The user must therefore learn how to use this diver's extension system and his full attention is required when handling the extension. Finally, the ball catches are systems which get dirty easily and which are not very reliable.